1. Field
The following description relates to a passive optical network (PON), and more particularly, to a wavelength tuning time measurement apparatus and method in a multi-wavelength passive optical network (MW PON).
2. Description of the Related Art
As optical communication technology is advanced and the demand for the Internet service increases rapidly, fundamental research on an optical access network has been conducted since the early 2000s, and thus introduction of a broadband convergence network (which directly connects an office or a central office (CO) to subscribers through an optical fiber) such as fiber to the home (FTTH) and fiber to the office (FTTO) is generalized. Herewith, research on next generation super high-speed large-scale optical access network technology is being actively done for responding to an explosive increase in traffic due to the spread of mobile Internet protocol (IP) terminals such as smartphones or tablet computers, the commercialization of an IP television (IPTV) service, and the spread of a multimedia broadcast/streaming service over the Internet.
As a method for efficiently providing a service to more subscribers with limited network resources, a time division multiplexing (TDM) technique and a wavelength division multiplexing (WDM) technique are being applied to optical access network technology. Recently, research is being done on an optical access network using a hybrid technique in which both the TDM technique and the WDM technique are applied. Attempts to apply an orthogonal frequency division multiplexing (OFDM) technique (which is mainly used in wireless communication at present) to the optical access network technology are also being actively made, which is an example of the hybrid technique in a broad sense.
Among the techniques, the WDM technique or the hybrid technique may perform communication using a plurality of wavelength bands, namely, a multi-wavelength. As the use of the Internet increases and demand for multimedia contents increases explosively, increasing a bandwidth of a network in a wired optical access network and a wireless network or a merged wired/wireless network thereof is becoming an increasingly important issue, and particularly, a technique using a multi-wavelength is attracting an attention as a type of method for solving the important issue. According to this, it is possible not only to provide a super high-speed communication service to many subscribers, but also to easily expand a communication capacity and the number of subscribers with an excellent communication security. Therefore, in the next generation super high-speed large-scale optical access network technology, an MW PON using the WDM technique or the hybrid technique is obtaining a great interest.
An MW PON system may include a service provider unit (hereinafter referred to as “an optical line terminal (OLT)”) installed in a CO, a user terminal unit or a number of subscriber units (hereinafter referred to as “an optical network unit (ONU)”) neighboring thereto, and a local node in which one or more optical multiplexers/de-multiplexers or light intensity splitters are installed or an optical distribution network (hereinafter referred to as “an optical distribution unit (ODN)”). In the MW PON system, a network configuration may be varied depending on the kind of used light source, for example, a spectrum-split light source, a wavelength-locked light source, or a wavelength-independent light source. Further, a wavelength of light used in the MW PON system may be fixed between an OLT and a specific ONU, or varied.
Active research on the use of a wavelength-variable light source is being done for efficiently utilizing wavelength resources in the MW PON, for example, a hybrid PON or a WDM PON using a wavelength multiplexing scheme. Using the wavelength-variable light source, it is possible to solve a problem caused by the production, installation, and management of light sources for each wavelength. In addition, it is possible to provide an efficient and user-convenient service in which load balancing is made by dynamically allocating a wavelength, or when a link is congested, a new link is established by quickly changing a current wavelength to another wavelength.
A wavelength varying operation or a wavelength tuning operation, in which a wavelength-variable light source stably generates light of a wavelength different from the original wavelength, is needed for communication between an OLT and each of ONUs using the wavelength-variable light source. Further, in the MW PON system, a wavelength tuning time may be changed depending on a mechanism, in which a wavelength is changed in the wavelength tuning operation, or a wavelength interval between channels to be changed. Therefore, the wavelength tuning time of the wavelength-variable light source should be importantly considered in a link establishment procedure of changing the existing wavelength to a new wavelength between the OLT and the ONU. Especially, in terms of the MW PON system in which an ODN includes a light intensity splitter instead of multiplexers for each wavelength, when the wavelength tuning time of the wavelength-variable light source is not sufficiently considered, the wavelength-variable light source operates in a state in which a wavelength is not completely changed, and can affect a channel of other wavelength. For this reason, an apparatus and a procedure are required for clearly defining the wavelength tuning time of the wavelength-variable light source and measuring the wavelength tuning time according thereto.